Biopsy studies on the natural sex reversal in Monopterus albus (Pisces: Teleostei)

A technique for the study of the ontogenetic development and the sequential changes in structure of the gonad of Monopterus albus during natural sex reversal was established by making successive biopsy examinations on gonadal tissue of individual animals at regular time intervals. Results obtained from the present investigation provided some direct and conclusive evidence that anatomical transformation from an ovary, through a transitory intersexual phase, to a testis occurred as a natural process in the life cycle of individuals in this species, and confirmed most of the previous observations derived from studies based upon body-size and sexuality correlation. This biopsy approach will form a basis for further investigations on the effects of various experimentations, such as hormone administration, hypophysectomy, photo-stimulation and thermo-stimulation, on sex differentiation and sex changes in this protogynous hermaphroditic fish.     

The ultrastructural and biosynthetic characteristics of steroidogenic cells in the gonad of Monopterus albus (Teleostei) during natural sex reversal

Summary The ultrastructural and biosynthetic characteristics of the steroid cells in the gonad of Monopterus albus have been studied. Ultrastructural features related to steroidogenesis have been identified in the interstitial Leydig cells, Sertoli cells, granulosa cells and thecal cells, and are especially abundant in the Leydig cells during the mid-intersexual phase. Steroidogenic ultrastructures in the Sertoli cells develop only during the maturation of the spermatogenic cysts, whereas in the granulosa and thecal cells, these features become obvious only during the maturation of the large oocytes. EM evidence also suggests a nutritive function for the Sertoli cells and the granulosa cells. Results of in vitro steroidogenic studies, using either testosterone or progesterone as a precursor, show a predominant conversion to androstenedione and 5-reduced compounds, and suggest a change in biosynthesis from 5-reduced products to androstenedione during sex reversal. 11-Ketotestosterone (11KT) has been identified, but not 11 -hydroxytestosterone. Production of 11 KT is high in the late intersexual and the male phases, but a lack of a marked variation in 11KT production between the early and the mid-intersexual phase suggests that this steroid is not a trigger for natural sex reversal in Monopterus.     

黄鳝性腺自然逆转过程中vasa基因的表达分析

本研究采用RNA反义探针原位杂交技术,对vasa基因在黄鳝(Monopterusalbus)性腺发育过程中的表达情况进行了分析。结果表明:vasamRNA在Ⅰ、Ⅱ、Ⅲ期卵母细胞的胞质中均匀分布,在Ⅳ、Ⅴ期卵母细胞中vasamRNA有向胞质外周皮层迁移集中的趋势,但不明显;退化的卵粒也呈现vasamRNA阳性反应;在Ⅲ、Ⅳ期卵巢的被膜中检测到带有vasa阳性信号的细胞,这些细胞可能是待向精原细胞分化、迁移到卵巢被膜上的原始生殖细胞(Primordialgermcell,PGC),在性逆转过程中这些PGC可能由卵巢被膜迁移到精小叶中并发育成精子;在成熟精巢中,vasa在精原细胞和初级精母细胞中表达。进一步采用碱性磷酸酶染色法分析黄鳝卵巢及精巢后发现:在卵巢中,除了卵母细胞外,卵巢被膜中也检测到了带有碱性磷酸酶阳性信号的细胞;在成熟精巢中,只在生殖腺囊内的雄性生殖细胞中检测到碱性磷酸酶,而精巢被膜中没有检测到带有碱性磷酸酶阳性信号的细胞。本研究结果初步表明:黄鳝的雄性生殖细胞可能起源于雌性阶段卵巢被膜中的原始生殖细胞[动物学报51(3):469-475,2005]。     

A study on the 3β- and 17β-hydroxysteroid dehydrogenase activities in the gonads of Monopterus albus (Pisces: Teleostei) at various sexual phases during natural sex reversal

Activities of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) in Monopterus gonads were studied at different sexual phases during natural sex reversal. Before sexual transformation, positive reactions for 3β-HSD in the follicular epithelium were found in the granulosa cells of some large, maturing follicles in some females during the breeding season. Weak reaction for this enzyme was also detected in some scattered interstitial cells found occasionally in some ovaries. At the intersexual and the male phases, intense 3β-HSD activities were demonstrated exclusively in the interstitial Leydig cells. No 17β-HSD activities were observable in the gonads at any stage of development. The reaction intensity of 3β-HSD in the interstitial cells exhibited a marked increase during the process of sex change from female to the intersexual and the male phases and there is a definite correlation with the density and nuclear size of these cells. It is concluded that in Monopterus , the granulosa cells in the ovary and the interstitial cells of the intersexual and male gonads are the major sites for the biosynthesis of oestrogens and androgens, respectively, and that the intensive development of interstitial tissue with increasing steroidogenic enzyme activities at the intersexual and male phases was directly related to the increase in androgen production in vitro reported previously. The occasional presence of some 3β-HSD positive interstitial cells in the ovary suggests that interstitial cell development might precede testicular lobule formation during natural sex reversal.     

Seasonal changes in the distribution of gonadal lipids and spermatogenetic tissue in the male phase of Monopterus albus (Pisces: Teleostei)

The gonad of Monopterus albus undergoes cyclical changes after the reversal of sex from female to male. The seasonally variable events include a prenuptial accumulation of cholesterol-positive lipid droplets in the cytoplasm of the interstitial cells when spermatogenetic activity is resumed in late February and early March. The development of the interstitial Leydig cells reaches a maximum in May just before spawning. There occurs a sudden depletion of the interstitial lipids during the breeding season in June at a time when the male animals exhibit active nuptial behaviour. After spermiation, the old interstitial cells degenerate, and during the succeeding phase of gonadal inactivity, become replaced by a new generation from connective tissue cells in the interstitium of the gonadal lamellae which gradually accumulate lipoidal material.
The lobular cycle comprises a postnuptial accumulation of amorphous intralobular lipids which become completely cleared in February when active spermatogenesis is restored. Spermatogenesis resumes shortly after spawning, but only advances as far as primary spermatocytes during the postnuptial period of inactivity.
The authors conclude that, as far as the seasonal variations in gonadal lipid distribution is concerned, the cycles in the gonad of the hermaphroditic teleost, M. albus , conform to the same pattern as those of the gonochoristic seasonal breeders studied.     

The atretic structures in the gonads of the rice-field eel (Monopterus albus) during natural sex-reversal

The gonad of the protogynous, hermaphroditic teleost, Monopterus albus were examined histologically at monthly intervals throughout one year. In particular, the epithelium of the maturing follicles of the female and the atretic follicles in the female, intersex and male were studied. Atretic follicles were common in the gonads and were classified as corpora atretica types 1 to 5 according to histological criteria. In addition, other regressive structures were observed in the gonads of some males. The histology and the frequency of occurrence of the atretic structures in the three sexual phases is described and discussed.     

Identification of Dmrt genes and their up-regulation during gonad transformation in the swamp eel (Monopterus albus)

The swamp eel is a teleost fish with a characteristic of natural sex reversal and an ideal model for vertebrate sexual development. However, underlying molecular mechanisms are poorly understood. We report the identification of five DM (doublesex and mab-3) domain genes in the swamp eel that include Dmrt2, Dmrt2b, Dmrt3, Dmrt4 and Dmrt5, which encode putative proteins of 527, 373, 471, 420 and 448 amino acids, respectively. Phylogenetic tree showed that these genes are clustered into corresponding branches of the DM genes in vertebrates. Southern blot analysis indicated that the Dmrt1–Dmrt3–Dmrt2 genes are tightly linked in a conserved gene cluster. Notably, these Dmrt genes are up-regulated during gonad transformation. Furthermore, mRNA in situ hybridisation showed that Dmrt2, Dmrt3, Dmrt4 and Dmrt5 are expressed in developing germ cells. These results are evidence that the DM genes are involved in sexual differentiation in the swamp eel.     

Patterns of gonad structure in hermaphroditic gobies (Teleostei Gobiidae)

Synopsis Hermaphroditism has been reported for a small number of gobiid fishes, but the extent of this sexual pattern within the family is not known. Gonad structure was examined in one or more species from twenty-one gobiid genera. No evidence of hermaphroditism was found in the species selected from 14 genera. Laboratory studies supported the conclusion of gonochorism for the examined species in four of them:Asterropteryx, Bathygobius, Gnatholepis, andPsilogobius. Currently, the absence of precursive testicular tissues associated with the ovary in females, in conjunction with no retained ovarian features in the testes of males, appear to be reliable indicators of a gonochoristic sexual pattern in gobiid fishes. Evidence for hermaphroditism was observed in seven genera:Eviota, Trimma, Fusigobius, Lophogobius, Priolepis, Gobiodon, andParagobiodon. Protogyny was experimentally confirmed inE. epiphanes, and the gonad structure in another nine of ten species ofEviota suggested either protogyny or protogynous tendencies. With the exception ofGobiodon andParagobiodon, which exhibited similar gonadal structure, ovarian and testicular structure varied considerably among the hermaphroditic genera examined, both with regard to the configuration and to the degree of development of ovarian and testicular tissues, or testicular tissue precursors. Findings of this study indicate that hermaphroditic gonad structure will prove to be a useful trait in determining evolutionary relationships within the Gobiidae.     

Variability of the behavioral laterality in Teleostei (Pisces)

Factors causing variability of behavioral laterality in Teleostei are reviewed. The laterality has been revealed in many fish species belonging to various families. The best ever demonstrated example of the laterality is the different use of the right and left eyes when a fish responds to different visual objects. Magnitude and sign of the laterality differ in fishes of different species, gender, and age. Also, an observed laterality depends on how familiar a stimulus is to fishes and what it means to them, as well as their motivational level and various behavioral traits. Therefore, comparisons of the laterality among different fish species should be based on experimental methods that also take into account those behavioral differences among them that are not directly linked to the laterality.     

Conus-like structure in the eye of the deep-sea teleost Radiicephalus elongatus (Pisces,Teleostei)

Summary A conus-like structure, the hyaloid conus, located on the optic nerve head of the mesopelagic deep-sea teleost Radiicephalus elongatus is described. The hyaloid conus consists of a tapering sheath of unpigmented, vascularized connective tissue enveloping the proximal part of the hyaloid artery which proceeds from the optic nerve head through the vitreous body to the ventrally located falciform process and lens muscles. The hyaloid artery passes through the hyaloid conus without giving off any branches. The conus vessels encircling the hyaloid artery receive arterial blood from the choroid via small arteries and are drained to the choroid by a single vein. The hyaloid conus is compared with the lacertilian conus papillaris. The function of the hyaloid conus is unknown. Because of its small dimensions relative to those of the eyeball and its few capillaries, it is unlikely that the hyaloid conus is a supplemental nutritive device for the retina.     

On the mechanism of air ventilaton in anabantoids (Pisces: Teleostei)

Summary Air ventilation in most Anabantoid species is diphasic, consisting of exhalation and inhalation. Exhalation is the release of air from the accessory breathing organs (suprabranchial chambers) through the mouth either into the water near the surface (e.g.,Ctenopoma) or directly into the atmosphere (e.g.,Osphronemus goramy). Inhalation, i.e., taking in fresh air through the mouth at the surface, immediately follows exhalation. X-ray films show (Figs. 5 and 6) that evacuation of the suprabranchial chambers during exhalation is total or nearly total. This, together with the fact that these chambers can contract at most to a very small extent, led to the conclusion that gas is replaced by water entering the chambers during exhalation and that this water is replaced by fresh air during inhalation. Further analysis of films, including conventional films showing the behavior of the opercular apparatus during air ventilation (Fig. 7), leads to a theory of a double-pumping mechanism responsible for air ventilation. This mechanism consists of the buccal apparatus and the opercular apparatus. It is suggested that both of these structures are able to act as both suction and pressure pumps, and thus air ventilation may be explained as the result of alternating activity of these two pumps.In the monophasic air ventilation characteristic of (adult)Anabas testudineus, there is no exhalation phase comparable to that of other Anabantoids. Therefore, no water enters the suprabranchial chambers, which remain filled with gas during the whole ventilation process (Fig. 10). Ventilation is limited to one phase comparable to inhalation in other Anabantoids.The structure of the accessory breathing organs (Fig. 1) and its progressive complication with growth (Fig. 4) were studied inOsphronemus goramy. The arrangement of the labyrinthine plates is in accordance with the requirements of transport of water and gas through the suprabranchial chambers. One plate (the inner plate, Fig. 1) separates these chambers into atrium, ventro-caudal, and dorso-caudal compartments, each with its own opening (valve). This organization seems essential for the transport of gas and water through the suprabranchial chambers and ensures that during exhalation, water flows into the chambers from above, so that while water is filling these chambers displaced gas can be sucked through the deep-lying pharyngeal openings into the expanding buccal cavity.Supported by the Deutsche Forschungsgemeinschaft     

Morphological development of the mouse gonad in tda-1 XY sex reversal

tda-1 XY sex reversal occurs when the Y chromosome of at least some populations of wild Mus musculus domesticus is placed on the C57BL/6J genomic background. Gross anatomical observations have previously revealed morphological similarities among fetal ovotestes of tda-1 and Tas-inherited XY sex reversals and BALB/cWt mosaic hermaphrodites. We studied the histology of tda-1 XY sex-reversed gonads, ranging in age from day 14 of gestation to adult. The obtained data revealed additional similarities with ovotestes of BALB/cWt mosaic hermaphrodites as well as with ovotestes of hermaphrodites found in XXSxr and XX/XY chimeras. It is proposed that ovotestes occurring in these various hermaphroditic conditions may be formed through a common pathway.     

黄鳝染色体Ag—NORS多态性的研究

采用PHA活体处理直接制片,对黄鳝染色体进行Giemsa染色、C-带及Ag-NORs等相继系列研究。结果发现,黄鳝的染色体Ag-NORs具有明显的个体特异性的数目多态、分布多态和形态多态现象。11尾被检测个体中,多态特征可分为4种类型。位于第3或第7号染色体臂内的次缢痕是Ag-NORs所在的区域,该区域分布有大量的结构异染色质,即Ag-NORs与C-带强阳性呈现严格的同步对应。本文根据实验结果,对黄鳝AS-NORs多态性的发生机制及其与结构异染色质的关系进行了探讨。     

黄鳝的繁殖生态学研究

以洞庭湖稻区黄鳝为调查研究对象 ,通过野外调查和室内实验系统研究了黄鳝的繁殖生态。对黄鳝的性腺发育周年变化、繁殖行为、自然产卵过程、产卵条件及繁殖洞穴的构造进行了观察和记录 ,产卵室是黄鳝繁殖洞穴特有的构造 ,繁殖洞穴泥土p H平均值为 6 .73± 1.0 12。亲鳝有护卵习性 ,通过对 30尾守洞亲鳝的性腺观察和切片验证 ,守洞鳝多为雄鳝 (占 6 1.3% ) ,少数为兼性偏雄性 (占 38.7% ) ,守洞鳝 1:0 0～ 2 :0 0全在外面活动 ,守洞鳝体长 L (cm)与体重 W (g)回归方程为 :W=1.2 5×10 - 2 L1 .4 2 (r=0 .76 )。人工模拟条件下 ,泡沫组受精卵的平均孵化率 (85 .2 % )极显著地高于对照组 (2 5 .4 % ) (t=8.18,t0 .0 5=2 .4 5 ) ,仔鱼平均成活率 (6 4 .0 % )显著高于对照组 (14 .0 % ) (t=3.73) ,同时对繁殖季节黄鳝为孵卵而所吐的泡沫的作用进行了分析。另外 ,证实了黄鳝产卵的最适放养密度为 2～ 3尾 / m2。为黄鳝的全人工繁殖和半人工繁殖提供了合理化的建议     

A gular plate in Pterothrissus (Pisces, Teleostei)

A gular is reported in Pterothrissus belloci Cadenat and P. gissu Hilgendorf (Albuloidei, Pterothrissidae).     

黄鳝血液生理参数的研究

报道了健康黄鳝血液的几项生理参数。结果 ,红细胞 2 .37× 10 12 L ,白细胞 4.16× 10 9L ,血栓球 6 1.6× 10 9L ,血红蛋白 134 .5 gL ,红细胞最大脆性 0 .35 % (NaCL溶液 ) ,血沉 1.0 5mmh ,凝血时间 1.75min。并将黄鳝的血液生理参数与其它几种鱼类作了对比分析